The most common type of surgical needle is a single use needle which is crimped to the end of a suture. The needle is used once and then discarded. It is preferable that the needle have a diameter that is only slightly larger than the suture.
The single use needle can be a "drilled end" needle. In this type of needle a concentric hole is formed, usually by drilling in the butt of the needle. The suture is placed in the hole. The needle is then crimped around the suture. The crimp must be strong enough to enable the suture to remain attached to the needle during the in-vivo placement of the needle and the passing of the suture through tissue.
After the suture approximates the tissue, it is frequently convenient to detach the needle so that the ends of the suture can be tied together without the needle(s). Cutting of the suture with scissors or a scapel is a convenient method of disengaging the needle. This requires an extra instrument and an extra manipulation. Some surgeons use commercially available pull-off needles. The pull-off values for these needles are in conformity with U.S. Pharmacopeia (abbreviated "USP" herein) requirements.
In addition to size of the needle and suture, which can effect the strength of the needle-suture attachment, other variables can be the surface smoothness of the suture and needle lubricants. Some needles are lubricated with a silicone rubber or polytetrafluoroethylene to reduce tissue drag in use. The needle hole can be filled with zylene or another volatile solvent during coating to reduce the penetration of the lubricant into the needle hole.
In many instances each needle-suture combination is nondestructively tested to a minimum pull-off value in routine production. Only those that pass a test load are accepted for further processing.
Conventional crimp operations are difficult to control. Usually, crimping is between dies that close to a fixed gap, and any variation in the crimp dies, the needle size, the hole size and the suture size changes the degree of crimp. Quality control is likewise difficult.
Other approaches such as crimping to a controlled pressure, or using a combined pressure and gap cycle have been considered. The usual approach is to increase the degree of crimp until the crimping shears off the suture on a test sample, then back off on the degree of crimp until the sutures are not sheared off, and pull-off above USP limits, and after testing a representative group of sutures, proceeding to production.
The attachment of surgical needles to surgical sutures is an ongoing mechanical problem which is most challenging. There is a continuous trend towards eyeless needles in which the end of the suture is fixed to the needle so that the suture is pulled axially through the tissue causing a minimum of trauma. The attachment must be one which (a) is predictably secure, (b) causes a minimum of damage to tissue, (c) is convenient for the using surgeon, (d) permits sterilization and (e) entails reasonable costs, so that the suture needle may be attached economically. The attachment must stand up under the rigors of manufacture, sterilization, storage, shipment and use.
In theory, if all process parameters are perfectly controlled, replicate results are obtained. In practice, so many factors enter that adequate control in production is easier to describe than accomplish.
To develop the background of this invention, the following references are disclosed:
U.S. Pat. No. 3,125,095 issued to D. Kaufman, G. Buccino and A. Glick on Mar. 17, 1964 and is entitled "Flexible Stainless Steel Sutures". This patent discloses generally the manufacture of a coated multifilament steel suture, and specifically in FIG. 3 and column 5, lines 19 to 30 the crimping of the same into a drilled end needle.
U.S. Pat. No. 4,054,144 issued to J. Hoffman and P. Marsland on Oct. 18, 1977 and is entitled "Short-Crimp Surgical Needle". Related U.S. Pat. Nos. 4,060,885 and 4,072,041 issued on Dec. 6, 1977 and Feb. 7, 1978, respectively. These patents respectively disclose a needle-suture combination, and a process and dies for manufacturing the same. These patents generally relate to the attaching of a surgical suture to a drilled end needle. There is also a thorough discussion with cited references relating to the background and development of the art.
All of the above cited U.S. patents are incorporated herein by reference.